Radiation Curable Compositions Useful in Image Projection Systems

ABSTRACT

A radiation-curable composition useful for the production of three-dimensional solid articles is provided. The radiation-curable composition comprises at least one hyperbranched poly(meth)acrylate compound, at least one light sensitizer, and at least one free radical polymerization initiator.

FIELD OF THE INVENTION

The present invention relates to radiation curable compositions usefulin light image projection systems. More preferably, the presentinvention relates to (meth)acrylate-based compositions that contain twoor more free radical photoinitiators in both the visible and UV lightranges.

BACKGROUND OF THE INVENTION

Image projection systems are a recent development in thethree-dimensional solid imaging field. Such systems are an alternativeto stereolithographic solid imaging systems using laser scanning. Imageprojection systems may use a combination of UV light and visible lightto initiate and complete photocuring of the three-dimensional solidarticles, objects, parts, prototypes, or the like. They are an extremelylow cost approach to solid imaging when compared to stereolithographicsystems that use more expensive laser beams to initiate photocuring. Theimage projection process may employ either an endless or a retractableflexible, light-permeable belt or film coated with a radiation curableresin that is moved through an exposure station where a digital lightprojector imagewise exposes the resin through the light-permeable beltor film to imagewise solidify and form a cured resin layer. After thisimagewise exposure and curing, the imaged and cured resin layer isseparated from the belt and remains adhered to the build platform on topof previously exposed layers. This process is then repeated until adesired three-dimensional object is made. Resin layers are repeatedlycoated onto the endless belt and then imagewise exposed. Each solidresin layer is then separated from the belt and remains adhered to thesupport platform with subsequent exposed layers until the completedobject is formed.

An example of an image projection system employing an endless belt isdisclosed in US Patent Application Publication No. 2007/0259066.Examples of image projection systems employing a retractable film aredisclosed in US Patent Application Publication Nos. 2008/01 69589 and2008/0206383. These latter patent applications relate to the V-FLASH®film transfer imaging system available from 3D Systems Corporation ofRock Hill, S.C. These patent applications are incorporated herein byreference in their entireties.

The curable resins used in such image projection systems need to have acombination of desirable properties. Preferably, such resins should havelittle or no surface tackiness and should have reduced adhesionproperties so they can be easily removed from the endless belt, yet havesufficient physical properties so that they form usefulthree-dimensional objects. Further, it is well known that UV curablestraight (meth)acrylate resins of this type generally have shrinkage anddistortion problems similar to mixed epoxy/acrylate resin systems.Trying to correct these shrinkage and distortion problems in straight(meth)acrylate resins systems can cause the photospeed of the resin toundesirably decrease. Still further, it is also desirable to produce adry part that the end user can handle without any danger ofsensitization resulting from skin contact with the formedthree-dimensional object. Examples of such curable resins are disclosedin U.S. Pat. No. 7,358,283, which issued on Apr. 15, 2008, which isincorporated herein by reference in its entirety. While such straight(meth)acrylate resins are suitable for use in making three dimensionalarticles with image projector systems, there is still a need for betterstraight (meth)acrylate resins that cure faster and more thoroughlywhile having better coating uniformity, especially on hard surfaces likeTEFLON-type transfer films disclosed in the above-noted patentapplications related to the V-FLASH system. The present invention offerssolutions to those and other needs.

BRIEF SUMMARY OF THE INVENTION

One aspect of the present invention is directed to a radiation-curablecomposition useful for the production of three-dimensional solidarticles by light image projection systems, said composition comprises:

-   (A) at least one hyperbranched poly(meth)acrylate compound;-   (B) at least one light sensitizer; and-   (C) at least one free radical polymerization initiator.

Still another aspect of the present invention is directed tothree-dimensional solid articles made from the above-noted curablecomposition by an image projection system.

Therefore, one aspect of the present invention is directed to aradiation-curable straight (meth)acrylate composition useful for theproduction of three-dimensional solid articles by image projectionsystems, said composition comprises:

-   (A) at least one hyperbranched polyester poly(meth)acrylate    compound;-   (B) at least one UV light sensitizer;-   (C1) at least one visible light range free radical polymerization    initiator; and-   (C2) at least one UV light range free radical polymerization    initiator.-   (D) at least one urethane poly(meth)acrylate compound;-   (E) at least one poly(meth)acrylate compound; and-   (F) at least one non-hyperbranched polyester poly(meth)acrylate    compound.

Still another aspect of the present invention is directed tothree-dimensional solid articles made from the above-noted curablecomposition by an image projection system.

The above compositions of the present invention offer severaladvantages. The compositions are easily released from various transferfilms and are cured relatively quickly to be tack free. Anotheradvantage of the present invention is to provide cured three-dimensionalobjects with a desirable combination of physical and mechanicalproperties. Another advantage is the present composition provides aresin material that permits the use of reliable image projectionprocesses to produce high quality three-dimensional parts. Stillfurther, the compositions of the present invention may have bettercoating properties on low surface tension surfaces such as TEFLON-likesurfaces.

DETAILED DESCRIPTION OF THE INVENTION

The term “(meth)acrylate” as used in present specification and claimsrefers to both acrylates and methacrylates.

The term “poly(meth)acrylate” as used in the present specificationrefers to both acrylates and methacrylates that have more than oneacrylate or methacrylate functionality. Examples include diacrylates,triacrylates, tetraacrylates, pentaacrylates, dimethacrylates,trimethacrylates, tetramethacrylates and pentamethacrylates.

The term “straight (meth)acrylate resin system” as used in the presentspecification refers to resin formulations that contain one or more(meth)acrylate compounds but no epoxy compounds and are useful formaking three dimensional solid articles, preferably with the use of aimage projector system.

It is to be understood that the term “light” as used in the presentspecification can mean electromagnetic radiation in the wavelength rangeincluding infrared, visible, ultraviolet and x rays, that when travelingin a vacuum moves with a speed of about 186,281 miles per second or300,000 kilometers per second. Accordingly, “light” as used hereinincludes but is not limited to any and all forms of actinic radiation.

The novel compositions of the present invention contain a mixture ofseveral separate components or compounds listed above. The compositionsmay contain these separate ingredients in any proportion that would beuseful as radiation-curable compositions in light image projectionsystems. These compositions may further optionally contain colorants andother additives. Preferably, the compositions of the present inventiondo not contain silicone poly(meth)acrylate compounds.

(A) Hyperbranched Poly(meth)acrylate Compounds

The first component of the composition of present invention is at leastone hyperbranched poly(meth)acrylate. From a structural standpoint,hyperbranched oligomers are quite different from typical oligomers usedin radiation cure applications. They have a “globular” morphology ratherthan the typical linear morphology. Because of these structuraldifferences, they possess beneficial properties for such curingapplications. See the Sartomer publication dated March 2008 by J. A.Klang entitled “Radiation Curable Hyperbranched Polyester Acrylates” fora detailed discussion of these compounds. For the present invention, apreferred example of this first component is SARTOMER CN2302hyperbranched polyester poly(meth)acrylate available from the SartomerCompany. Other hyperbranched polyester acrylate compounds that may besuitable for the present invention include CN2300, CN2301, CN2303, andCN2304, all available from Sartomer and discussed in the Klang article.Of course, other hyperbranched polyester poly(meth)acrylate compoundsand mixtures of hyperbranched compounds may be used if they are able toproduce useful three-dimensional articles. In certain preferredembodiments of the present invention, the hyperbranched polyesterpoly(meth)acrylate compound constitutes about 3% to about 20% by weightof the total composition.

(B) Light Sensitizers

The second component of the compositions of the present invention is atleast one light sensitizer compound. Light sensitizers have been usedbefore in stereolithographic resin composition as an optional compound.In the compositions of the present invention, sensitizers are used toshorten the surface curing time period so that through-put time formaking a three-dimensional article is improved. Preferably, the at leastone light sensitizer is at least one UV light sensitizer. One preferredUV light sensitizer is Additol ITX isopropyl thioxanthone available fromCytec. Of course, other thioxanthone UV light sensitizers as well asother useful light sensitizers and mixtures of sensitizers includingmixtures of visible light sensitizers and UV light sensitizers may beused in the present invention for making three-dimensional articles. Incertain preferred embodiments of the present invention, thesensitizer(s) constitutes about 0.005% to about 1% by weight of thetotal composition.

(C) Free Radical Polymerization Initiators (Photoinitators)

The third component of the compositions of the present invention is atleast one free radical polymerization initiator (also calledphotoinitiators). While a single photoinitiator may be used in thisinvention, it is preferred to use a combination of at least one visiblelight range photoinitiator and at least one UV light rangephotoinitiator, especially when an image projecting system is used toproduce the three-dimensional object. In certain preferred embodimentsof the present invention, the total amount of photoinitiators is about1% to about 10% by weight of the total resin composition.

(C1) Visible Light Range Free Radical Polymerization Initiators

The visible light range free radical polymerization initiator(s) can beany free radical polymerization initiator that will start a free radicalreaction when exposed to radiation in the spectral range including about350 nanometers to about 500 nanometers. The preferred visible lightrange free radical polymerization initiator(s) isbis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide which is available asIRGACURE 819 form Ciba Specialty Chemicals, Inc.

The visible light range free radical polymerization initiator(s) ispreferably present in an amount from about 0.5% to about 7% by weight,based on the total weight of the composition; more preferably, fromabout 1% to about 5% by weight of the total composition.

(C2) UV Light Range Free Radical Polymerization Initiators

The UV light range free radical polymerization initiator(s) can be anyfree radical polymerization initiator(s) that will start a free radicalreaction when exposed to radiation in the UV light spectrum (includingabout 260 nanometers to about 380 nanometers). The preferred UV lightrange free radical polymerization initiator(s) is 1-hydroxycyclohexylphenyl ketone that is available as IRGACURE I-184 from Ciba SpecialtyChemicals, Inc.

The UV light range free radical polymerization initiator(s) ispreferably present in amount from about 0.5% to about 7% by weight ofthe total composition; more preferably from about 1% to about 6% byweight of the total composition.

(D) Urethane Poly(meth)acrylate Compounds

The compositions of the present invention may also preferably contain atleast one urethane poly(meth)acrylate compound. Preferably, thiscompound is a urethane di(meth)acrylate compound. More preferably, thiscompound is a urethane diacrylate oligomer such as Sartomer CN9011available from Sartomer Company of Exton, Pa.

The urethane poly(meth)acrylate compound or compounds preferablyconstitute from about 10% to 40% by weight of the total composition;more preferably, from about 20% to about 35% by weight of the totalcomposition.

(E) Poly(meth)acrylate Compounds

The composition of the present invention may also preferably contain atleast one poly(meth)acrylate compound. This component (E) is differentthan the other components in this composition. Preferably, thiscomponent is a diacrylate monomer that may be polymerized by freeradicals. More preferably, this component is tricyclodecane dimethanoldiacrylate monomer such as Sartomer SR833S available from SartomerCompany. This compound can be used in a variety of applications whereinboth flexibility and toughness are required.

The poly(meth)acrylate compound or compounds preferably constitute fromabout 20% to about 55% by weight of the total composition; morepreferably, from about 25% to about 50% by weight of the totalcomposition.

(F) Non-Hyperbranched Polyester Poly(meth)acrylate Compounds

Besides the above-described components, the present invention may alsopreferably include at least one non-hyperbranched polyesterpoly(meth)acrylate compound.

Preferably, the non-hyperbranched polyester poly(meth)acrylate compoundor compounds constitute from about 5% to about 30% by weight of thetotal composition; more preferably, from about 10% to about 25% byweight of the total composition.

One preferred embodiment of the present invention includes two suchcompounds. One compound is a low viscosity amine-modified polyacrylatepolyester oligomer such as Ebecryl 83 available from UCB Chemicals Corp.of Smyrna, Ga. The second compound is an amine-modified polyestertetraacrylate such as SARTOMER 80 also available from the SartomerCompany. In one preferred embodiment, the combination of these twoamine-modified non-hyperbranched polyester poly(meth)acrylate compoundsis employed.

(G) Other Optional Additives

If necessary, the resin composition for image applications according tothe present invention may contain other materials in suitable amounts,as far as the effect of the present invention is not adversely affected.Examples of such materials include coloring agents such as pigments anddyes, fillers, antifoaming agents, leveling agents, thickening agents,flame retardants, and antioxidants.

One preferred class of additives is colorants, particularly pigments.These are included to add color to the resultant cured product. Twosuitable pigments are Penn Color 9W7 white pigment and Penn Color 9S4blue pigment, both available from Penn Color Inc. of Doylestown, Pa. Itis preferred to use such pigments in amounts from about 0.005% to about1% by weight of the total curable resin composition.

Another preferred optional material is a leveling agent such as one ofthe MODAFLOW leveling agents available from Cytec Industries. If used,it is preferably present in a amount from about 0.05% to about 1% byweight of the total curable resin composition.

Still another preferred optional component is fumed silica. A preferredone is AEROSIL R202 available from Evonik Degussa GmbH. If used, it ispreferably present in an amount from about 0.25% to about 2% by weight.This component provides better coating uniformity to the compositions ofthe present invention on very low surface tension surfaces used in theV-FLASH systems described in the above-noted US patent applications.

Formulation Preparation

The novel compositions can be prepared in a known manner by, forexample, premixing individual components and then mixing these premixes,or by mixing all of the components using customary devices, such asstirred vessels, in the absence of light, if desired, at slightlyelevated temperature. Preferably, the preferred formulations of thepresent invention are mixed together in a suitable manner and thenplaced in light-tight cartridges employed with the V-FLASH film transferimaging systems described above and in the US patent applications citedabove.

Process for Making Cured Three-Dimensional Articles

These compositions of the present inventions can be made into curedthree-dimensional solid articles with any suitable image projectionsystem, including those that employ BenQ PB7230 projectors. Becausethese compositions contain both a visible light range free radicalphotoinitiator and a UV light range free radical photoinitiator, it isdesirable to use a UV light source in conjunction with an imageprojection system. The UV light source can be used (i.e., the resinsource can be exposed to that UV light source) before or after ortogether with the visible light source of the image projection system.The UV light source removes the tackiness of parts in a post-curing ofbuilt parts while the parts are in the image projection system, thuscreating a dry part handling system for the operator. Of course, aperson ordinarily skilled in the art would be aware that it isnecessary, for each chosen light source, to select the appropriatephotoinitiator and species of the above-noted components as well as runthe image projection system at the preferred operations conditions toachieve the most desired results.

It is believed that such cured products are useful in the same manner asthe cured products of various stereolithographic systems.

The present invention is further described in detail by means of thefollowing comparisons and example. All parts and percentages are byweight and all temperatures are degrees Celsius unless explicitly statedotherwise.

COMPARISONS 1 AND 2 AND EXAMPLE 1

The trade names of the components as indicated in the Examples

TABLE 1 List of material identities and chemical compositions. TRADENAMES CHEMICAL DESIGNATION SARTOMER CN9011 Aliphatic urethane diacrylateoligomer SARTOMER SR 833S Tricyclodecane dimethanol diacrylate monomerCYTEC EBECRYL 83 Amine-modified multi-functional acrylated polyesteroligomer SARTOMER CN2302 Hyperbranched polyester acrylate oligomer CYTECEBECRYL 350 Silicone polyacrylate CIBA IRGACURE I-1841-Hydroxycyclohexyl phenyl ketone CIBA IRGACURE I-819 Bis(2,4,6-trimethyl benzoyl)- phenylphosphine oxide PENN COLOR 9W7 Whitepigment paste CIBA IRGACURE I-907 2-methyl-1-(4-methylthio)phenyl-2-morpholino-propan-1-one CYTEC EBECRYL 80 Amine-modified polyestertetraacrylate CYTEC ADDITOL ITX Isopropyl thioxanthone CYTEC MODAFLOWAcrylic oligomer DEGUSSA AEROSIL R202 Fumed silica SARTOMER CN2881Highly branched multifunctional polyester acrylate

The formulations indicated in the Comparisons and Example below wereprepared by mixing the components with a stirrer at 60° C. in a glasscontainer until all photoinitiators were dissolved and a homogeneouscomposition was obtained. These dissolved formulations of theComparisons 1 and 2 and Example 1 were then added into separate V-FLASHsystem cartridges of the type described in the above-noted US PatentApplications and then each formulation was used to produce differentthree-dimensional objects in a V-FLASH system of the type described inthe above-noted US Patent Applications under the same operatingconditions. The V-FLASH system was equipped with BenQ PB7230 projectorvisible light image projection system and a TEFLON-like transfer film.All of the produced three-dimensional objects were then cleaned withisopropyl alcohol and then completely cured with a UV light source.Visual observations as noted below were made of these producedthree-dimensional objects.

COMPARISON 1

The following components are similar to those disclosed in U.S. Pat. No.7,358,283 and were mixed to produce a homogeneous liquid composition:

TABLE 2 List of components, percentage by weight. COMPONENT PERCENTAGE(by wt.) SARTOMER CN9011 23.74 SARTOMER SR 833S 35.61 CYTEC EBECRYL 8323.63 SARTOMER CN2302 9.50 UCB EBECRYL 350 1.00 CIBA IRGACURE I-907 3.56CIBA IRACURE I-819 2.85 PENN COLOR 9W7 0.11 Total 100

Three dimensional articles produced by above procedure with theformulation of this Comparison 1 were observed to consistently havemissing features. These missing features resulted from observed defectsoccurring in the resin coating films such as fisheye, craters, and thelike. These defects were believed to be caused by dewetting of the resincoating films from the TEFLON-like transfer film. These defects wouldprevent these articles from being used commercially.

COMPARISON 2

The following components are similar to the compositions disclosed inU.S. Pat. No. 7,358,283 and were mixed to produce a homogeneous liquidcomposition:

TABLE 3 List of all components, parts by weight and percentage byweight. COMPONENT PERCENTAGE (by wt.) SARTOMER CN9011 28.28 SARTOMER SR833S 39.01 CYTEC EBECRYL 83 37.72 SARTOMER CN2881 8.03 CYTEC MODAFLOW0.52 CIBA IRGACURE I-184 1.96 CIBA IRGACURE I-819 1.52 CYTEC ADDITOL ITX0.09 Total 100.00

Three dimensional articles produced by above procedure with theformulation of this Comparison 2 were observed to consistently havemissing features. These missing features resulted from observed defectsoccurring on the resin coating films such as fisheye, craters, and thelike. These defects are believed to be caused by dewetting of the resincoating films from the TEFLON-like transfer film. These defects couldprevent these articles from being used commercially.

EXAMPLE 1

The following components were mixed to produce a homogeneous liquidcomposition:

TABLE 4 List of all components, parts by weight and percentage byweight. COMPONENT PERCENTAGE (by wt.) SARTOMER CN9011 28.28 SARTOMER SR833S 39.01 CYTEC EBECRYL 83 4.88 CYTEC EBECRYL 80 9.75 SARTOMER CN23029.75 CIBA IRGACURE I-184 3.66 CIBA IRGACURE I-819 2.93 PENN COLOR 9W70.59 CYTEC MODAFLOW 0.24 CYTEC ADDITOL ITX 0.05 DEGUSSA AEROSIL R2020.88 Total 100.00

Three-dimensional articles produced by the above procedure with theformulation of this Example 1 were observed to consistently have fullfeatures. Also, no defects were observed on the resin coating films inthe V-FLASH system. No dewetting of the resin on the TEFLON-liketransfer film was observed. The absence of these defects would allowthese articles to be used commercially.

While the invention has been described above with reference to specificembodiments thereof, it is apparent that many changes, modifications,and variations can be made without departing form the inventive conceptdisclosed herein. Accordingly, it is intended to embrace all suchchanges, modifications and variations that fall within the spirit andbroad scope of the appended claims. All patent applications, patents,and other publications cited herein are incorporated by reference intheir entirety.

1. A radiation-curable composition useful for the production ofthree-dimensional solid articles, the composition comprising: (A) atleast one hyperbranched poly(meth)acrylate compound; (B) at least onelight sensitizer; and (C) at least one free radical polymerizationinitiator.
 2. The composition of claim 1 wherein the at least onehyperbranched poly(meth)acrylate compound is at least one hyperbranchedpolyester polyacrylate compound.
 3. The composition of claim 1 whereinthe at least one hyperbranched polyester poly(meth)acrylate compound ispresent in an amount from about 3% to about 20% by weight, based on thetotal amount of the composition.
 4. The composition of claim 1 whereinthe at least one light sensitizer is at least one thioxanthanone UVlight sensitizer.
 5. The composition of claim 1 wherein the lightsensitizer is present in an amount from about 0.005% to about 1% byweight, based on the weight of the total composition.
 6. The compositionof claim 1 wherein the at least one free radical polymerizationinitiator is present in an amount from about 1% to about 10% by weight,based on the total amount of the composition.
 7. A radiation-curablestraight (meth)acrylate composition useful for the production ofthree-dimensional solid articles by image projection systems, thecomposition comprising: (A) at least one hyperbranched polyesterpoly(meth)acrylate compound; (B) at least one UV light sensitizer; (C1)at least one visible light range free radical polymerization initiator;(C2) at least one UV light range free radical polymerization initiator.(D) at least one urethane poly(meth)acrylate compound; (E) at least onepoly(meth)acrylate compound; and (F) at least one non-hyperbranchedpolyester poly(meth)acrylate compound.
 8. The composition of claim 7wherein the at least one hyperbranched polyester poly(meth)acrylatecompound is present in an amount from about 3% to about 20% by weight,based on the total amount of the composition.
 9. The composition ofclaim 7 wherein the at least one UV light sensitizer is at least onethioxanthanone UV light sensitizer.
 10. The composition of claim 7wherein the light sensitizer is present in an amount from about 0.005%to about 1% by weight, based on the weight of the total composition. 11.The composition of claim 7 wherein the visible light range free radicalpolymerization initiator(s) is present in an amount from about 0.5% toabout 7% by weight, based on the weight of the total composition. 12.The composition of claim 7 wherein the UV light range polymerizationinitiator(s) is present in an amount from about 0.5% to about 7% byweight, based on the weight of the total composition.
 13. Thecomposition of claim 7 wherein the at least one urethanepoly(meth)acrylate compound is urethane diacrylate oligomer.
 14. Thecomposition of claim 7 wherein the at least one urethanepoly(meth)acrylate compound is present in an amount from about 10% toabout 40%, based on the weight of the total composition.
 15. Thecomposition of claim 7 wherein the at least one poly(meth)acrylatecompound is at least one diacrylate monomer.
 16. The composition ofclaim 7 wherein the at least one poly(meth)acrylate compound is presentin an amount from about 20% to about 55%, based on the weight of thetotal composition.
 17. The composition of claim 7 wherein the at leastone non-branched polyester poly(meth)acrylate compound is at least oneamine-modified non-branched polyester polyacrylate compounds.
 18. Thecomposition of claim 7 wherein non-branched polyester poly(meth)acrylatecompound(s) is present in an amount from about 5% to about 30%, based onthe weight of the total composition.
 19. A radiation-curable straight(meth)acrylate composition useful for the production ofthree-dimensional solid articles by image projection systems, thecomposition comprising: (A) about 3% to about 20% of at least onehyperbranched polyester poly(meth)acrylate compound; (B) about 0.005% toabout 1% of at least one light sensitizer; (C1) about 0.5% to about 7%of at least one visible light range free radical polymerizationinitiator; (C2) about 0.5% to about 7% of at least one UV light rangefree radical polymerization initiator; (D) about 10% to about 40% atleast one urethane poly(meth)acrylate compound; (E) about 20% to about55% at least one poly(meth)acrylate compound; and (F) about 5% to about30% of at least one non-hyperbranched polyester poly(meth)acrylatecompound, all percentages based on the weight of the total composition.20. The composition of claim 1 9 wherein the composition additionallycontains about 0.005% to about 1% by weight of at least one pigment-typecolorant.
 21. The composition of claim 19 wherein the compositionadditionally contains about 0.05% to about 1% by weight of at least oneleveling agent.
 22. The composition of claim 1 9 wherein the compositionadditionally contains about 0.25% to about 2% by weight of at least onefumed silica.